Redworm elimination in an integrated fixed-film activated sludge reactor

Two pilot-scale biological nutrient removal bioreactors were operated side by side under selected flow rate conditions. One reactor was operated under an integrated fixed-film activated sludge (IFAS) reactor configuration, and the second reactor was operated under a conventional activated sludge reactor configuration. The relatively high dissolved oxygen (DO) and low food-to-microorganism ratio created a favourable environment for the proliferation of redworm identified as Aeolosoma hemprichi in the IFAS reactor from day 116, which led to significant deterioration on ammonia removal in the IFAS reactor. The removal efficiencies of chemical oxygen demand (COD) and phosphorus were not significantly affected by the redworm bloom. Several strategies were applied to eliminate the redworms from the IFAS reactor. The most effective strategy was shutting off the DO supply in the aerobic zone and stopping the influent feed for 48 h. Finally, it took about 1·5 months for the IFAS reactor to recover from performing the worm elimination strategy.